Risks of explosion mixing O2 and H2 in Ar magnetron plasma?

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Discussion Overview

The discussion revolves around the potential risks of explosion when mixing oxygen (O2) and hydrogen (H2) in an argon (Ar) magnetron sputtering discharge. Participants explore the implications of introducing these gases simultaneously in a plasma environment, particularly focusing on the conditions of the discharge, energy dynamics, and gas flow rates.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the risk of explosion due to the simultaneous presence of O2 and H2 in the discharge, under specific conditions of pressure and RF power.
  • Another participant suggests calculating the energy released from the reaction of H2 and O2 to assess the explosion risk compared to the energy input from the RF generator.
  • A third participant agrees with the need for a calculation of reaction enthalpy based on the number of moles involved, emphasizing the importance of the vacuum conditions and the sturdiness of the chamber.
  • A further contribution questions the potential applied across the tungsten and the plasma, as well as the flow rates of the gases, drawing on experience with ionization in plasma systems and noting that explosion risks are typically linked to excessive gas flow.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the explosion risk, with differing views on the importance of energy calculations, gas flow rates, and the specifics of the discharge conditions. Multiple competing perspectives remain on how to evaluate the safety of the setup.

Contextual Notes

Limitations include the lack of specific data on the flow rates of the gases and the potential applied across the discharge, which may influence the risk assessment. The discussion also highlights the dependence on the definitions of safety thresholds in plasma environments.

atomica68
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I am interested in adding simultaneously O2 and H2 in a magnetron sputtering discharge ignited in Ar at a pressure of 3*10-2 mbar. The discharge is driven by a RF generator (13.56 MHz, 60 - 120W). The target is W. Can anyone told me if I can expect at any explsion to apear due to simultanoously presence of O2 and H2 in the discharge?
Thank you in advance for responses.
 
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I think you can figure this out yourself. How much energy would be released if all of the H2 and O2 in your experiment reacted? How does this compare with the amount of energy going into the experiment from the RF generator?
 
Exactly my thought - simple calculation of reaction enthalpy given number of moles of the substance should tell you if there is any risk involved. Especially taking into account you work in vacuum, so the chamber must be quite sturdy.
 
What is the potential applied across the tungsten and the plasma? Also, what is the flow rate of the two gasses? I work with ICPMS and have experience dealing with argon plasma ionization, but ours is at 1500W (~10,000 K) and potentials of 5 - 10V. The hydrogen and oxygen should ionize instantly going into the plasma. They will want to recombine afterwards as one would expect, but if the potential is high enough, you may accelerate the ions fast enough to hit the target before then. The concept is the same with ICPMS where the ions are accelerated and focused with lenses to prevent recombination. Typically, when tuning a plasma to produce less recombination, a lower flow rate is used. Explosion is not typically seen unless too much gas is being pumped in.